Modify Points of a Multires Modifier through Python
try this:
import bpy
import bmesh


bpy.ops.mesh.primitive_cube_add(enter_editmode=False, align='WORLD', location=(0, 0, 0), scale=(1, 1, 1))
bpy.ops.object.modifier_add(type='MULTIRES')
bpy.ops.object.multires_subdivide(modifier=&quot;Multires&quot;, mode='CATMULL_CLARK')
bpy.ops.object.multires_subdivide(modifier=&quot;Multires&quot;, mode='CATMULL_CLARK')

active_obj = bpy.context.active_object

depsgraph = bpy.context.evaluated_depsgraph_get()
multires_mesh = depsgraph.objects[active_obj.name].data

# test to modify
print(len(multires_mesh.vertices))  # It Will be 98 Points. Multires!
for v in multires_mesh.vertices:
    v.co[0] *= 2.0
    
bm2 = bmesh.new()
bm2.from_mesh(multires_mesh)
    

result: